1. Field of the Invention
The present invention generally relates to a reverse rotation control apparatus for a two-cycle engine which makes it possible to drive or run a motor vehicle equipped with the two-cycle engine exchangeably in forward or rearward (backward) direction by reversing rotation of the engine. More specifically, the present invention is concerned with a reverse rotation control apparatus for a two-cycle engine mounted on a motor vehicle which apparatus can realize a reverse rotation control processing with inexpensive hardware structure without incurring degradation in the exhaust gas composition and the ignition performance of the motor vehicle equipped with the two-cycle engine.
2. Description of Related Art
In general, a four-cycle engine mounted on a motor vehicle such as a passenger car or the like is equipped with a clutch and a gear box at an output side of the engine for deriving the output power thereof through the medium of the clutch and the gear box.
However, in the case of small-size motor vehicles for specific purposes such as snowmobiles, all-terrain vehicles and the like, a two-cycle engine of an inexpensive structure is mounted. In this conjunction, it is further noted that in case of these motor vehicles, the space for installing or accommodating the engine is limited.
Such being the circumstances, no gear box is ordinarily installed as the reverse rotation control apparatus for the two-cycle engine in these types of the motor vehicles, wherein the output torque of the engine is derived by way of a centrifugal-type automatic transmission implemented in the form of a V-belt transmission.
Consequently, the motor vehicle can be driven only in the forward direction. Thus, manpower is required for moving the motor vehicle backwards or rearwards as is in the case where the motor vehicle is to be taken out from a garage or it is to be disburden from a carrier such as a lorry, giving rise to a problem that the motor vehicle is very inconvenient to handle.
For evading the problem mentioned above, it has been proposed that a clutch and a gear box are provided equally for the motor vehicle equipped with the two-cycle engine by affording a sufficient space for installation of the two-cycle engine so that the traveling direction of the motor vehicle can be changed over between the forward direction and the backward or rearward direction by manipulating a gear change lever, as in the case of the four-cycle engine.
For having a better understanding of the concept underlying the present invention, a hitherto-known or conventional reverse rotation control apparatus for a two-cycle engine of a motor vehicle will be reviewed in some detail.
FIG. 4 is a block diagram showing schematically and generally a configuration of a prior art reverse rotation control apparatus for a two-cycle engine of a motor vehicle in which a conventional gear box is employed. Referring to FIG. 4, an internal combustion engine (hereinafter referred to simply as the engine) 1 driven in two cycles (i.e., two-cycle engine) is installed on a motor vehicle (not shown). The engine 1 has an output shaft 2 which rotates in one direction as indicated by an arrow, wherein a driving torque generated by the engine 1 is outputted through the medium of a clutch 3 and a gear box 4. At this juncture, it should be mentioned that the gear box 4 is provided with a back gear train for allowing the motor vehicle to be driven backwardly or rearwardly.
Furthermore, a change lever 5 is provided in the gear box 4 for allowing a driver to manually change over gear trains. A rotation sensor 6 for detecting the engine speed (rpm) as well as angular position of a crank shaft (crank angle) of the engine is implemented in the form of an electromagnetic pickup device or the like and provided in association with the output shaft of the engine 1. A rotation signal SG derived from the output of the rotation sensor 6 is inputted to an ignition control unit 10 which may be constituted by a microprocessor or microcomputer.
The ignition control unit 10 is so designed or programmed as to arithmetically determine control timings for the engine 1 for issuing an ignition signal P on the basis of operating state information which includes not only the rotation signal SG mentioned above but also other signals derived from the outputs of other various sensors (not shown).
An ignition coil 11 is realized in the form of a transformer having a primary winding and a secondary winding for generating in response to the ignition signal P a secondary voltage boosted up upon interruption of the primary current, whereby a high voltage for firing is applied to a spark plug 12 of the engine 1. In this conjunction, it is to be noted that the engine 1 is subjected to rotation control in a predetermined direction by controlling the ignition timing on the basis of the rotation signal SG.
In the two-cycle engine of a motor vehicle equipped with the conventional reverse rotation control apparatus as shown in FIG. 4, the rotation output or output torque of the engine 1 can be reduced as desired by means of the gear box 4 while the driving direction of the motor vehicle can be changed over between the forward direction and the rearward or backward direction with the aid of the back gear train.
However, with the arrangement shown in FIG. 4, difficulty will be encountered in assuring a space around the engine 1 for affording accommodation and installation of the gear box 4. In particular, in the case of the snowmobile and the all-terrain vehicle mentioned previously, difficulty is encountered in making available an engine room for accommodating therein the engine 1 itself. Consequently, additional provision of the gear box 4 will incur remarkable increase in the manufacturing cost of these types of motor vehicles.
At this juncture, it is noted that the two-cycle engine has a feature that the crank shaft can be rotated in any one of the forward direction or the reverse direction by selectively controlling the ignition timing, differing from the four-cycle engine.
In actuality, a reverse rotation control apparatus for a two-cycle engine has been realized by making use of the above-mentioned feature. By way of example, there is disclosed in U.S. Pat. No. 5,036,802 issued in 1997 such an reverse rotation control apparatus for a two-cycle engine of a motor vehicle which makes it possible to drive the motor vehicle either in the forward direction or in the backward direction through the reverse rotation control of the engine 1 by using a centrifugal-type automatic transmission (not shown) without resorting to the use of the gear box 4.
In the case of the reverse rotation control apparatus disclosed in the U.S. Patent specification cited just above, when a driving direction of a motor vehicle equipped with a two-cycle engine is to be reversed, a driver manipulates a rotation reversing lever in a normal rotation state of the engine 1 (corresponding to e.g. forward traveling of the motor vehicle). Then, the ignition control unit 10 lowers the rotation speed (rpm) of the engine 1 by forcibly causing misfire to take place in the engine 1. When the engine rotation speed has thus been lowered to a predetermined rotation speed (e.g. 500 rpm) which is suited for the reverse rotation control (i.e., control for reversing the rotating direction of the engine), the ignition timing at which the ignition signal P is applied is caused to advance excessively beyond a normal advance control position (lying within a range of 5.degree. to 30.degree. before the top dead center TDC in terms of crank angle, i.e., BTDC 5.degree. to 30.degree.). With the excessive advance control for the ignition timing described above, the ignition timing is set, for example, at BTDC 40.degree. (i.e., at the crank angle of 40.degree. before the top dead center or BTDC 40.degree.), for thereby allowing the engine 1 to transit from the normal rotation state (corresponding to e.g. forward running of the motor vehicle) to the reverse rotation state (corresponding to e.g. rearward traveling direction of the motor vehicle).
Thereafter, the ignition control unit 10 regards the reverse rotation direction as the normal rotation direction and the ignition signal P is generated at the ordinary ignition timing for sustaining continuously the reverse rotation state of the engine 1. Thus, the motor vehicle can be driven backwardly or in the reverse direction. Parenthetically, when the engine 1 is to be restored from the reverse rotation state to the normal rotation state, the control process similar to that described above is carried out by regarding the current rotating direction of the engine (i.e., the reverse rotation) as the normal rotating direction.
With the reverse rotation control apparatus described above, manufacturing cost of the motor vehicle can certainly be reduced significantly because the gear box 4 can be spared. However, because the engine rotation number or engine speed (rpm) is lowered to a predetermined rotation number at which the rotation of the engine 1 can be reversed by resorting to the misfire control technique described above, unburnt gas is discharged from the engine 1 during the misfire control process, giving rise to a problem.
Furthermore, during the misfire control process, deposition of fuel components on a discharge electrode of the spark plug 12 is likely to occur, as a result of which ignition performance of the engine 1 may possibly be degraded at a succeeding ignition timing, to a disadvantage.
As can be understood from the foregoing, the reverse rotation control apparatus for the two-cycle engine for a motor vehicle suffers a problem that when the gear box 4 such as shown in FIG. 4 is employed, there arises the necessity for ensuring a space for installation of the gear box 4 around the engine 1, which will of course lead to increasing of the cost.
On the other hand, the system for the reverse rotation control of the engine 1 in which the engine rotation number is once lowered by resorting to the misfire control process and then advances in excess the ignition timing, as is disclosed in U.S. Pat. No. 5,036,802, suffers such problem that degradation may be brought about in the exhaust gas composition as well as in the ignition performance of the engine.